Amplifiers are subject to reduced gain when feedback between the input and output signals occurs. Conventional transistor amplifiers are especially subject to instability from feedback. Such feedback is inherent in transistors due to the presence of parasitic and junction capacitance between the collector-base or the drain-gate terminals.
For example, in a cordless telephone system, a handset generates, amplifies and then transmits the signals to a base station. Any instability or decrease in gain of the amplifier, however, may decrease the quality of the transmitted signal, and as a result, can decrease the performance of the telephone system.
The inclusion of an inductive element between the output and the input terminals can reduce the amount of amplifier feedback at specific frequencies. The presence of the inductive element creates a parallel resonant circuit with the feedback capacitance which presents a high impedance feedback path at the resonant frequency. This technique is known as neutralization. A neutralized amplifier will demonstrate improved stability and increased gain because of the reduction of capacitive feedback.
The technique of neutralization in discrete circuits is not widespread as the feedback is typically minimized at a single frequency. Also, the presence of an inductive element can increase the feedback at lower frequencies and result in instability.